1. Field
The disclosed concept pertains generally to separable contacts and, more particularly, to stationary contact assemblies. The disclosed concept also pertains to circuit interrupters including a stationary contact assembly. The disclosed concept also pertains to transfer switches including stationary contact assemblies.
2. Background Information
Transfer switches are well known in the art. See, for example, U.S. Pat. Nos. 7,569,949; 7,239,045; 6,849,967; 5,397,868; 5,210,685; 4,894,796; and 4,747,061. Transfer switches operate, for example, to transfer a power consuming load from a circuit with a normal power supply to a circuit with an auxiliary power supply. Applications for transfer switches include stand-by applications, among others, in which the auxiliary power supply stands-by if the normal power supply should fail. Facilities having a critical requirement for continuous electric power, such as hospitals, certain plant processes, computer installations, and the like, have a standby power source, often a diesel generator. A transfer switch can control electrical connection of utility power lines and the diesel generator to facility load buses. In many installations, the transfer switch automatically starts the standby generator and connects it to the load bus upon loss of utility power, and reconnects the utility power to the load bus if utility power is reestablished.
A transfer switch typically can comprise a pair of circuit interrupters combined with a drive input and a linkage system. The preferred types of circuit interrupters have been molded-case switches and molded-case circuit breakers because these types are commercially available in a wide array of sizes and are relatively economical compared to other options. The preferred type of drive input depends on the application for the transfer switch. Usually motors or solenoids are preferred, but at other times there is a clear preference for manually-operated mechanisms.
A typical automatic transfer switch (ATS) includes a housing, an operating mechanism, a first line bus, a second line bus, a load bus, a first line movable contact, a second line movable contact, a fixed contact assembly, and a control device. The operating mechanism, first line movable contact, second line movable contact, fixed contact assembly, and control device are disposed within the housing. Only one of the first and second movable contacts engages the fixed contact assembly at a time. That is, in the normal operating configuration, the first movable contact is in a second position, and is capable of providing electricity to a system load from a primary power source, and the second movable contact is in a first position. If the need arises, the first movable contact is moved into the first position while the second movable contact moves into the second position. The transfer can occur almost instantaneously. In this configuration, a secondary power source is capable of providing electricity to the system load. Operation (i.e., positioning of the first and second movable contacts) is performed by the operating mechanism.
It is known for circuit breakers to include a set of main contacts, an operating mechanism for opening the set of main contacts, a trip device to actuate the operating mechanism to trip the set of main contacts open in response to certain overcurrent conditions, a set of secondary contacts, and a remotely controllable actuator to control the open and closed states of the set of secondary contacts.
A known circuit breaker includes line and load terminals, and first and second circuit breaker mechanisms. Each of the first and second circuit breaker mechanisms includes a corresponding set of separable contacts in series between circuit breaker line and load terminals, a corresponding operating mechanism for moving the corresponding set of separable contacts between open and closed positions, and a corresponding trip mechanism cooperating with the corresponding operating mechanism for moving the corresponding set of separable contacts from the closed to the open position thereof.
U.S. Pat. No. 7,368,677 discloses a circuit breaker pole including a pair of main contacts that include a stationary main contact and a movable main contact. The movable main contact is carried by a moving conductor assembly. This moving conductor assembly includes a plurality of contact fingers, which are mounted in spaced axial relation on a pivot pin secured in a contact carrier. The contact carrier is rotated about pivots by an operating mechanism. A movable main contact is fixed to each of the contact fingers at a point spaced from the free end of the finger. The portion of the contact finger adjacent the free end forms a moving arcing contact or “arc toe”. A stationary arcing contact is provided on the confronting face of an integral arcing contact and runner mounted on a line side conductor. The stationary arcing contact and arc toe together form a pair of arcing contacts.
Automatic transfer switch power contactors preferably provide extensive endurance life. Typically, the stationary contacts thereof have superior anti-welding and temperature profiles.
There is room for improvement in stationary contact assemblies.
There is also room for improvement in a circuit interrupter employing a stationary contact assembly.
There is further room for improvement in a transfer switch employing stationary contact assemblies.